Automattic (the company behind WordPress) is doing the development of buddypress

No they aren’t! They may have nabbed the lead developer and possibly copyrighted the name but they aren’t ‘doing’ the development; it’s an open source project and the development is lead by a small group of volunteers.

@durkkooistra – cool Arras on BP. Nice demo. I suggest changing font-size of sidebar widgets text/lists to the same font-size for content like it is on Arras original. Btw, the theme download link on the link you gave goes to 404. Correct link

@mercime – Wow, I have trouble locating the CSS responsible for the big font. There are so many css files on so many locations, even with firebug I cant figure it out. Anybody that can give me some pointers?
“I suggest changing font-size of sidebar widgets text/lists to the same font-size for content like it is on Arras original”

Er you’ve used #container twice best to either lose the second or change it to #content-wrap and it’s best not to state explicit dimensions unless a need to so the inner element doesn’t need width:660px just let it default to 100% of it’s parent and then you can use padding or margins safely.

The font issue is possibly due to the text being written to an anonymous line box or at least to a div without any semantic element -in some cases – text or character data should never really be written directly to an element such as ‘div’, in others it’s defaulting to the reset.css font-sizing grouping whereas elements such as item-list-title have fixed px sizes described.

@hnla said it, with you’ve got #wrapper #main #container #container #content divs buddypress component pages. As for font-size which should be 12px throughout per original Arras theme, you have font-size 14px in your default.css carried over into your theme.